The National Weather Service declared Tuesday, Sept. 22, an Ozone Action Day for the Houston-Galveston area. League City falls within the alert zone.

Ozone pollution levels are expected to reach concentrations classified as "unhealthy for sensitive groups" through Tuesday evening, according to NWS Houston.

The Texas Commission on Environmental Quality (TCEQ) also issued the alert for Galveston and Brazoria counties, the Houston Chronicle reported.

High temperatures in the mid-to-high 90s are fueling the problem. The day's high could challenge Houston's daily record of 100 degrees, set on this date in 2005, according to the Chronicle.

The alert expires Tuesday evening.

Ground-level ozone forms when emissions from gasoline engines react with heat and sunlight, according to the Houston Chronicle's report on TCEQ guidance. The NWS advised residents to schedule outdoor activities for early morning or late evening and to limit driving or carpool when possible.

Residents can also help by combining errands, avoiding drive-thru lanes, conserving energy and keeping vehicles properly maintained, according to TCEQ guidance reported by the Chronicle.

NWS Houston posted on Sept. 21 that heat indices would reach triple digits, adding that air quality could reach unhealthy levels for sensitive groups.

Relief on the way

Drier air is expected to arrive Thursday as a weak frontal boundary moves through the region, according to the NWS. That shift should bring a slight drop in temperatures and near-zero rain chances.

A milder pattern could follow by the weekend. If current forecast models hold, afternoon highs may settle into the lower-to-middle 90s, with overnight lows dipping into the upper 60s and lower 70s north of Houston, the Chronicle reported.

Rain chances are forecast to rise again Sunday, Sept. 27, and into the following week.